1. Field of the Invention
The present invention relates to a tape spool or reel. More specifically, it relates to an improvement in tape spools to be assembled in belt-driven tape cartridges.
2. Description of the Prior Art
Computers which read and write data on magnetic tape require rapid acceleration and deceleration of the tape. The belt-driven tape cartridge described in U.S. Pat. No. 3,692,255 (Von Behren) has been found best suited to meet this requirement. However, it is not without its limitations.
The belt-driven tape cartridge, first marketed in 1972, was made to meet the density and speed requirements at that time. Since then, the original 1/4 inch wide (6.35 mm), one mil thick (0.025 mm) tape, driven at 30 inches (762 mm) per second, has become available in widths from 0.150 inches (3.81 mm) to 0.250 inches (6.35 mm), is as thin as 0.6 mil (0.015 mm) and may be driven at 120 or more inches (3048 mm) per second. Data densities have increased by nearly an order of magnitude. The high density of data on the tape is made possible by multiple independent, parallel tracks spaced across the width of the tape. The higher tape speeds and densities have introduced the possibility of the tape drifting up or down with respect to the tape head, causing head-to-data-track misalignment. Spool positioning and stability is critical to maintaining the tape in a readable position. The tape, and therefore the spool, must be prevented from floating in relation to the base of the cartridge.
A non-oscillating spool is described in U.S. Pat. No. 4,523,727 (Morioka). The spool's oscillation is decreased or eliminated by biasing against the top of the cartridge housing using a "wear button" on the top of the spool and a spring incorporated in the upper flange of the spool. The spool is maintained at a constant distance relative to the top of the cartridge housing.
Due to different rates of thermal expansion of plastic materials of which the cartridge housing is usually made and the metal base, warpage can occur in the housing, causing deflection of the tape path. Since the base is the critical plane of reference, it is desirable to assure that the base is the point of reference from which the tape and spool are maintained at a constant distance. It is to this end that the present invention is directed.